chat: rename the pi chat transport + model list to chat (Stage 4b/1)

Pure rename, no behavior change. Moves the misnamed "pi" chat harness into the
chat namespace:

- api/pi/{websocket,session-manager,types,logger,list-models} → api/chat/
- merge api/pi/rest.ts into api/chat/chat.ts (/pi/models → /chat/models,
  /pi/stt → /chat/stt); drop the piRestRouter mount
- PiEvent → ChatEvent, piWebsocket → chatWebsocket, listPiModels → listChatModels
- WS route /api/pi/chat/ws → /api/chat/ws, provider tag 'pi' → 'chat'
- frontend: useChat/useAudioRecording URLs, usePiModels→useModels /
  useVisiblePiModels→useVisibleModels / useEnabledPiModels→useEnabledModels,
  'PI_MODELS' query key → 'CHAT_MODELS', attachments provider 'pi-mono' → 'chat'

The /pi-mono provider/harness settings router is renamed separately (next commit).
Note: the WS route change requires the mobile app to point at /api/chat/ws.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/workspaces/state/src/index.ts

@@ -2,7 +2,7 @@ export { useSettings, DEFAULT_SETTINGS } from './useSettings';
 export type { UseSettingsType, UserSettings, UserState } from './useSettings';
 export { useUserState } from './useUserState';
 export { useDashboardState } from './useDashboardState';
-export { usePiModels, useVisiblePiModels, useUserVisibleModels, useEnabledPiModels, modelKey } from './useModels';
+export { useModels, useVisibleModels, useUserVisibleModels, useEnabledModels, modelKey } from './useModels';
 export type { ModelOption } from './useModels';
 export { useAccessPolicy } from './useAccessPolicy';
 export { useClaudeSessions, useChatPwds } from './useClaudeSessions';

src/workspaces/state/src/useModels.ts

@@ -23,19 +23,19 @@ export function getHostHome(): string {
   return globalHostHome;
 }
 
-export function usePiModels() {
+export function useModels() {
   const client = useClient();
   const { isAuthenticated } = useAuth();
 
   const { data: models = [] } = useQuery<ModelOption[]>({
-    queryKey: ['PI_MODELS'],
+    queryKey: ['CHAT_MODELS'],
     enabled: isAuthenticated,
     queryFn: async () => {
       const data = await client.get<{
         models: ModelOption[];
         providerNames?: Record<string, string>;
         hostHome?: string;
-      }>('/pi/models');
+      }>('/chat/models');
 
       if (data.providerNames) {
         globalProviderNames = data.providerNames;
@@ -54,8 +54,8 @@ export function usePiModels() {
 }
 
 /** Filter models by system-wide access policy. New providers pass through. */
-export function useVisiblePiModels() {
-  const models = usePiModels();
+export function useVisibleModels() {
+  const models = useModels();
   const { policy } = useAccessPolicy();
   const allowed = policy.allowedModels;
 
@@ -74,8 +74,8 @@ export function useVisiblePiModels() {
 
 /** Models visible to the current user: system policy (members) or all (admins), minus per-user hidden. */
 export function useUserVisibleModels() {
-  const allModels = usePiModels();
-  const policyModels = useVisiblePiModels();
+  const allModels = useModels();
+  const policyModels = useVisibleModels();
   const { user } = useAuth();
   const { settings } = useSettings();
 
@@ -90,8 +90,8 @@ export function useUserVisibleModels() {
 }
 
 /** Strict filtering — only explicitly allowed models, no "new provider" passthrough. */
-export function useEnabledPiModels() {
-  const models = usePiModels();
+export function useEnabledModels() {
+  const models = useModels();
   const { policy } = useAccessPolicy();
   const allowed = policy.allowedModels;